Plate fin heat exchangers generally comprise a plurality of plates and a plurality of fins extend between and may be secured to each adjacent pair of plates. The fins may be secured to the plates by brazing, welding, diffusion bonding etc. Alternatively the fins may not be secured to the plates. The fins are defined by corrugated plates. In plate fin heat exchangers the fins define the passages for the flow of fluids to be put into heat exchange relationship.
Primary surface heat exchangers generally comprise a plurality of plates and a plurality of spacers extend between each adjacent pair of plates to separate the plates. In primary surface heat exchangers the plates define passages for the flow of fluids to be put into heat exchange relationship.
Gas turbine engines comprise a compressor, a combustion chamber and a turbine arranged in flow series. The compressor compresses air and supplies it to the combustion chamber. Fuel is burnt in air in the combustion chamber to produce hot gases, which drive the turbine. The turbine drives the compressor and also drives a generator, a pump, a shaft or other load.
Heat exchangers are used in industrial gas turbine engines to return heat from the hot gases leaving the gas turbine engine to the compressed air leaving the compressor before it enters the combustion chamber. These heat exchangers are also known as recuperators, or regenerators. The recuperator heat exchanger increases the efficiency of the gas turbine engine and the hotter the air entering the combustion chamber the greater is the fuel saving.
The use of a spiral heat exchanger for a gas turbine engine recuperator is known from our European patent EP0753712B1 and this may be a plate fin type heat exchanger or a primary surface type heat exchanger.
A spiral heat exchanger, for example, is manufactured from two sheets of metal, which are wound together into a spiral and the edges of the sheets of metal are joined together. The sheets of metal may be stainless steel for low temperature spiral heat exchangers or nickel base alloy for high temperature spiral heat exchangers.
The outer ends of the two sheets of metal are joined to the last turn, or wrap, of the sheets to provide a seal to prevent pressurised fluid leaking out of the spiral heat exchanger. Additionally external attachments have to be secured to the axial ends of the spiral heat exchanger.
One problem with the manufacture of the spiral heat exchangers is sealing the outer ends of the metal sheets and at the same time allowing external attachments to be secured to the axial ends of the spiral heat exchanger.
One possible alternative is to provide an axially extending sealing weld between the outer ends of the two sheets of metal and the last turn, or wrap, of the sheets to provide the seal and then providing circumferentially extending welds between the axial ends of the spiral heat exchanger and two thicker metal rings. However, it is difficult to provide an axially extending sealing weld between two relatively thin metal sheets and the weld may blow through the sheet underneath to produce a hole and scrap the spiral heat exchanger. Also, it is difficult to provide the circumferentially extending welds between relatively thick metal rings and relatively thin metal sheets, because the heat transmitted from the relatively thick metal rings is likely to overheat the relatively thin metal sheets and produce a hole. Furthermore, the fit between the metal rings and the axial ends of the spiral heat exchanger is important and the circumferences have to match perfectly to achieve good circumferentially extending welds.